Ticket #1890 (closed task: moved)

We need a general-purpose way to associate metadata with objects. (SciJava Common's ObjectService is not quite appropriate: it stores objects onto lists associated with a type hierarchy.)

The StashService API will take a list of objects to use as a (weak) key, and a value to associate with that list of objects. So it is just a thread-safe HashMap which takes care of aggregating keys into a single StashKey object with WeakReferences to the key objects.

Once we have this service, we can use it for extensible metadata annotations of arbitrary data objects. For example, we can save derived data such as min/max values, histograms, statistics, measurements and more.